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Ventricular dynamics is a main determinant of the augmentation index: An in in vivo and in silico study

Research output: Chapter in Book/Report/Conference proceedingMeeting abstract

Original languageEnglish
Title of host publication14th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease
PublisherQueen Mary, University of London
Pages12
Number of pages1
Published2019
Event14th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease - Imperial College London, London, United Kingdom
Duration: 11 Apr 201912 Apr 2019
https://www.sems.qmul.ac.uk/events/bvbcd2019/

Conference

Conference14th International Symposium on Biomechanics in Vascular Biology and Cardiovascular Disease
CountryUnited Kingdom
CityLondon
Period11/04/201912/04/2019
Internet address

King's Authors

Abstract

Introduction
The role of pulse wave reflections in the increase of the augmentation pressure and, in turn, pulse pressure(PP) with ageing has been recently challenged as recent studies have highlighted the potential importance ofventricular ejection properties in determining blood pressure pulsatile components [1,2]. The first systolicshoulder (P1) of the pressure waveform is proportional to the product between the aortic pulse wave velocity(PWV) and aortic flow at time of P1 (U1) [3], and the usual peak pressure (P2) to the product between PWVand the volume of blood (V2) ejected at the time of P2 [4]. Both V2 and U1 can be approximated respectivelyby stroke volume (SV) and peak flow (Umax). Assuming proportionality between proximal and distal PWV andnoticing the close relationship between the augmentation index (AIx) and the ratio P2/P1, we investigate therelationship between AIx and a new index based entirely on ventricular mechanics, QIx, defined as SV/Umax.
Methods
The study involved patients from a normotensive (n=164, 126 men, age 49±8 years, blood pressure 110±16/69±10 mmHg, means±SD) and hypertensive (n=156, 83 men, age 46±17 years, blood pressure 130±23/83±13 mmHg) cohort. Reflected waves were quantified using the reflection coefficient Γ, i.e. the ratio of backward to forward pressure component. A Least Absolute Shrinkage and Selector Operator (LASSO) analysis was performed to statistically identify the main contributors to AIx among a set of cardiac and arterial parameters (Age, PWV, Γ, QIx, MBP, PP). To determine the relative contribution to AIx of arterial (Γ) and cardiac (QIx) properties, variations of AIx with QIx for an approximately fixed Γ were assessed, and vice versa. A sensitivity analysis of changes in AIx to QIx and Γ was also performed using an in silico model of blood flowin the larger arteries of the upper thoracic aorta.
Results
The LASSO analysis identified QIx, MBP and Γ as the main determinants of AIx with standardised coefficients of 0.32, 0.22 and 0.17, respectively (p>0.001 in each case). In vivo studies confirmed QIx was more correlatedthan Γ with AIx (Pearson coefficient, R= 0.71 vs R=0.53 in the normotensive group; R=0.52 VS R=0.37 in the hypertensive group). The sensitivity analysis also confirmed QIx have a greater impact on AIx than Γ.
Conclusions
We have proposed a new index based entirely on ventricular ejection dynamics and studied its relationship with AIx. The results of this part-in-silico/part-in-vivo study further challenge the role of reflection waves in the increase of AIx, as our new index was as correlated, if not more, to AIx than Γ.

References
[1] Torjessen AA, Wang N, Larson MGn Hamburg NM, Vita JA, Levy D, Benjamin EJ, Vasan RS, Mitchell GF,Forward and backward wave morphology and central pressure augmentation in men and women in theFramingham Heart Study, Hypertension, 64(2):259-265, 2014
[2] Fok H, Guilcher A, Li Y, Brett S, Shah A, Clapp B, Chowienczyk P, Augmentation Pressure Is Influenced byVentricular Contractility/Relaxation Dynamics, Hypertension, 63(5):1050-1055, 2014
[3] Vennin S, Mayer A, Li Y, Fok H, Clapp B, Alastruey J, Chowienczyk P. Noninvasive calculation of the aorticblood pressure waveform from the flow velocity waveform: a proof of concept, Am J Physiol Heart CircPhysiol, 309(5):H969-76, 2015
[4] Vennin S, Li Y, Willemet M, Fok H, Gu H, Charlton P, Alastruey J, Chowienczyk P. Identifying hemodynamicdeterminants of pulse pressure. A combined numerical and physiological approach, Hypertension, 70(6):1176-1182, 2017

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